Application of force feedback on an input device to urge its operator to command an articulated instrument to a preferred pose

ABSTRACT

A medical robotic system includes an entry guide with articulated instruments extending out of its distal end. A controller is configured to command manipulation an articulated instrument in response to operator manipulation of an associated input device while generating a force command to the input device that nudges the operator to command the instrument to a preferred pose. When a transition is to occur between first and second preferred poses, one is phased in while the other is phased out. Virtual barriers may be imposed to prevent the articulated instrument from being commanded to an undesirable pose.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 13/292,760 (filed Nov. 9, 2011), now U.S. Pat. No. 9,492,927, which is a continuation-in-part to U.S. application Ser. No. 12/704,669 (filed Feb. 12, 2010), now U.S. Pat. No. 8,918,211, each of which is incorporated herein by reference.

U.S. application Ser. No. 13/292,760 (filed Nov. 9, 2011) is also a continuation-in-part to U.S. application Ser. No. 12/613,328 (filed Nov. 5, 2009), now U.S. Pat. No. 9,084,623, which is a continuation-in-part to U.S. application Ser. No. 12/541,913 (filed Aug. 15, 2009), now U.S. Pat. No. 8,903,546, each of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to medical robotic systems and in particular, to a method and system applying force feedback on an input device to urge its operator to command an articulated instrument to a preferred pose.

BACKGROUND

Medical robotic systems such as teleoperative systems used in performing minimally invasive surgical procedures offer many benefits over traditional open surgery techniques, including less pain, shorter hospital stays, quicker return to normal activities, minimal scarring, reduced recovery time, and less injury to tissue. Consequently, demand for such medical robotic systems is strong and growing.

One example of such a medical robotic system is the DA VINCI® Surgical System from Intuitive Surgical, Inc., of Sunnyvale, Calif., which is a minimally invasive robotic surgical system. The DA VINCI® Surgical System has a number of robotic arms that move attached medical devices, such as an image capturing device and Intuitive Surgical's proprietary ENDOWRIST® articulating surgical instruments, in response to movement of input devices by a surgeon viewing images captured by the image capturing device of a surgical site. Each of the medical devices is inserted through its own minimally invasive incision into the patient and positioned to perform a medical procedure at the surgical site. The incisions are placed about the patient's body so that the surgical instruments may be used to cooperatively perform the medical procedure and the image capturing device may view it without their robotic arms colliding during the procedure.

To perform certain medical procedures, it may be advantageous to use a single entry aperture, such as a minimally invasive incision or a natural body orifice, to enter a patient to perform a medical procedure. For example, an entry guide may first be inserted, positioned, and held in place in the entry aperture. Articulated instruments such as an articulated camera instrument and a plurality of articulated surgical tool instruments, which are used to perform the medical procedure, may then be inserted into a proximal end of the entry guide so as to extend out of its distal end. Thus, the entry guide accommodates a single entry aperture for multiple instruments while keeping the instruments bundled together as it guides them toward the work site.

A number of challenges arise in medical robotic systems using such a bundled unit, however, because of the close proximity of the articulated camera and tool instruments. For example, because the camera instrument has proximal articulations (e.g., joints) that are not visible from the distal tip camera view, the surgeon can lose track of the current state of such articulations when moving the camera and consequently, their available range of motion. Also, when the articulations of the camera and tool instruments are out of view of the camera and therefore, not visible to the surgeon through its captured images, the surgeon may inadvertently drive links of the tools and/or camera instruments to crash into one another while telerobotically moving the articulated instruments to perform a medical procedure. In either case, the safety of the patient may be jeopardized and the successful and/or timely completion of the medical procedure may be adversely impacted.

OBJECTS AND SUMMARY

Accordingly, one object of one or more aspects of the present invention is a medical robotic system, and method implemented therein, that urges an operator to command a preferred pose for normal mode operation of an articulated instrument, which serves as a biasing point for operator commanded movement of the articulated instrument during normal operation of the instrument.

Another object of one or more aspects of the present invention is a medical robotic system, and method implemented therein, that applies force feedback on an input device to urge its operator to command the posing of an articulated instrument to a preferred pose with smooth transition to the preferred pose.

Another object of one or more aspects of the present invention is a medical robotic system, and method implemented therein, that applies force feedback on an input device to urge its operator to command the posing of an articulated instrument to a first preferred pose and then smoothly transition to a second preferred pose according to an activation signal.

These and additional objects are accomplished by the various aspects of the present invention, wherein briefly stated, one aspect is a method for urging operator manipulation of an input device to command an articulated instrument to a preferred pose, the method comprising: generating a commanded pose of the articulated instrument in response to operator manipulation of an input device; generating first force commands for a plurality of degrees of freedom of the input device so as to be indicative of a difference between a first preferred pose and the commanded pose; and applying the first force commands to the plurality of degrees of freedom of the input device by phasing in their application according to a first activation signal.

Another aspect is a medical robotic system comprising: an input device; an articulated instrument; and a processor configured to generate a commanded pose of the articulated instrument in response to operator manipulation of the input device, generate first force commands for a plurality of degrees of freedom of the input device so as to be indicative of a difference between a first preferred pose and the modified commanded pose, and command application of the first force commands on the plurality of degrees of freedom of the input device so as to phase in their application according to a first activation signal.

Additional objects, features and advantages of the various aspects of the present invention will become apparent from the following description of its preferred embodiment, which description should be taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a medical robotic system utilizing aspects of the present invention.

FIG. 2 illustrates a perspective view of a distal end of an entry guide with a plurality of articulated instruments extending out of it in a medical robotic system utilizing aspects of the present invention.

FIGS. 3-4 respectively illustrate top and right side views of articulated instruments extending out of a distal end of an entry guide in a medical robotic system utilizing aspects of the present invention.

FIG. 5 illustrates a block diagram of interacting components of an articulated instrument manipulator and an articulated instrument as used in a medical robotic system utilizing aspects of the present invention.

FIG. 6 illustrates a block diagram of an instrument controller for operator commanded movement of an articulated instrument in a medical robotic system utilizing aspects of the present invention.

FIG. 7 illustrates a side view of an articulated instrument extending out of a distal end of an entry guide in a preferred pose for normal operation as used in a medical robotic system utilizing aspects of the present invention.

FIG. 8 illustrates a side view of an articulated instrument extending out of a distal end of an entry guide in a preferred pose for retraction back into the entry guide as used in a medical robotic system utilizing aspects of the present invention.

FIG. 9 illustrates a block diagram of a simulated instrument block of the instrument controller of FIG. 6 as used in a medical robotic system utilizing aspects of the present invention.

FIG. 10 illustrates a block diagram of pose data and pose nudging blocks of the instrument controller of FIG. 6 as used in a medical robotic system utilizing aspects of the present invention.

FIG. 11 illustrates activation signals for normal mode operation and retraction mode as a function of time as used in a medical robotic system utilizing aspects of the present invention.

FIG. 12 illustrates a block diagram of the retraction mode nudging block of FIG. 10 as used in a medical robotic system utilizing aspects of the present invention.

FIG. 13 illustrates a block diagram of the normal mode nudging block of FIG. 10 as used in a medical robotic system utilizing aspects of the present invention.

FIG. 14 illustrates a block diagram of the force converter block of FIGS. 12 and 13 as used in a medical robotic system utilizing aspects of the present invention.

FIG. 15 illustrates a flow diagram of a method for modifying a commanded pose of an articulated instrument by applying a virtual barrier as a constraint as usable in a method for urging operator manipulation of an input device to command the articulated instrument to a preferred pose utilizing aspects of the present invention.

FIG. 16 illustrates a flow diagram of a method for generating a retraction mode activation signal usable in a method for urging operator manipulation of an input device to command the articulated instrument to a preferred pose utilizing aspects of the present invention.

FIG. 17 illustrates a flow diagram of a method for generating a normal mode deactivation signal usable in a method for urging operator manipulation of an input device to command the articulated instrument to a preferred pose utilizing aspects of the present invention.

FIG. 18 illustrates a flow diagram of a first embodiment of a method for urging operator manipulation of an input device to command an articulated instrument to a preferred pose utilizing aspects of the present invention.

FIG. 19 illustrates a flow diagram of a second embodiment of a method for urging operator manipulation of an input device to command an articulated instrument to a preferred pose utilizing aspects of the present invention.

FIG. 20 illustrates a flow diagram of a third embodiment of a method for urging operator manipulation of an input device to command an articulated instrument to a preferred pose utilizing aspects of the present invention.

FIG. 21 illustrates a flow diagram of a fourth embodiment of a method for urging operator manipulation of an input device to command an articulated instrument to a preferred pose utilizing aspects of the present invention.

FIG. 22 illustrates a block diagram of an alternative instrument controller for operator commanded movement of an articulated instrument in a medical robotic system utilizing aspects of the present invention.

FIG. 23 illustrates a block diagram of a “phase-in” nudging block providing a first nudging force command which is to be phased-in as a force to be applied against an input control device, as used in a medical robotic system utilizing aspects of the present invention.

FIG. 24 illustrates a block diagram of a “phase-out” nudging block providing a second nudging force command which is to be phased-out as a force being applied against an input control device, as used in a medical robotic system utilizing aspects of the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a block diagram of a medical robotic system 100. An entry guide (EG) 200 is configured to be inserted through an entry aperture such as a minimally invasive incision or a natural body orifice in a Patient. Articulated instruments such as a first articulated surgical tool (TOOL1) 231, second articulated surgical tool (TOOL2) 241, and an articulated stereo camera (CAM) 211 may be inserted through and extend out of a distal end of the entry guide 200. As shown in FIG. 2, the camera 211 has a stereo pair of image capturing devices 311, 312 and a fiber optic cable 313 (coupled at its proximal end to a light source) housed in its tip. The surgical tools 231, 241 have end effectors 331, 341. Although only two tools 231, 241 are shown, the entry guide 200 may guide additional tools as required for performing a medical procedure at a work site in the Patient. Additional details on the articulated instruments 211, 231, 241 are provided in reference to FIGS. 3 and 4 below.

Each of the devices 231, 241, 211, 200 is manipulated and controlled by its own manipulator and controller. In particular, the articulated camera instrument 211 is manipulated by a camera manipulator (ECM) 212 which is controlled by camera instrument controller (CTRLC) 213, the first articulated surgical tool 231 is manipulated by a first tool manipulator (PSM1) 232 which is controlled by tool instrument controller (CTRL1) 233, the second articulated surgical tool 241 is manipulated by a second tool manipulator (PSM2) 242 which is controlled by tool instrument controller (CTRL2) 243, and the entry guide 200 is manipulated by an entry guide manipulator (EGM) 202 which is controlled by entry guide controller (CTRLG) 203. The controllers 203, 233, 243, 213 are implemented in processor 102 as master/slave control systems as described in reference to FIG. 6 below.

Each of the articulated instrument manipulators 232, 242, 212 is a mechanical assembly that carries actuators and provides a mechanical, sterile interface to transmit motion to its respective articulated instrument. Each articulated instrument 231, 241, 211 is a mechanical assembly that receives the motion from its manipulator and, by means of a cable transmission, propagates it to the distal articulations (e.g., joints). Such joints may be prismatic (e.g., linear motion) or rotational (e.g., they pivot about a mechanical axis). Furthermore, the instrument may have internal mechanical constraints (e.g., cables, gearing, cams and belts, etc.) that force multiple joints to move together in a pre-determined fashion. Each set of mechanically constrained joints implements a specific axis of motion, and constraints may be devised to pair rotational joints (e.g., joggle joints). Note also that in this way the instrument may have more joints than the available actuators.

The entry guide manipulator (EGM) 202 is usable to robotically insert and retract the entry guide 200 into and out of the entry aperture. It may also be used to robotically pivot the entry guide 200 in pitch, roll and yaw relative to a longitudinal axis of the entry guide 200 about a pivot point (also referred to as a remote center “RC”). A setup arm may be used to hold and position the entry guide 200 so that its remote center RC is positioned at the entry aperture.

Two input devices 108, 109 are provided for manipulation by a Surgeon. Each of the input devices 108, 109 may be selectively associated with one of the devices 211, 231, 241, 200 so that the associated device may be controlled by the input device through its controller and manipulator. The Surgeon (or an Assistant) may perform such selection in a conventional manner, such as interacting with a menu on a Graphical User Interface (GUI), providing voice commands recognized by a voice recognition system, inputting such associations into the system 100 using an input device such as a touchpad, or interacting with special purpose buttons provided on the input devices 108, 109. Using any one of such association mechanisms, a select input is generated and provided to a multiplexer (MUX) 280, which is implemented in the processor 102. The value of the select input (e.g., combination of 1's and 0's) indicates which association (i.e., cross-switching) is selected.

For example, a first value for the select input to the multiplexer 280 places the left and right input devices 108, 109 in “tool following modes” wherein they are respectively associated with the first and second surgical tools 241, 231 so the Surgeon may perform a medical procedure on the Patient while the entry guide 200 is locked in place. In this configuration, the multiplexer 280 cross-switches to respectively connect output and input 251, 252 of the input device 108 to input and output 260, 261 of the tool controller 243; and respectively connect output and input 253, 254 of the input device 109 to input and output 268, 269 of the tool controller 233.

When the camera 211 is to be repositioned by the Surgeon, either one or both of the left and right input devices 108, 109 may be associated with the camera 211 using a second value for the select input so that the Surgeon may move the camera 211 through its controller 213 and manipulator 212. Similarly, when the entry guide 200 is to be repositioned by the Surgeon, either one or both of the left and right input devices 108, 109 may be associated with the entry guide 200 using a third value for the select input so that the Surgeon may move the entry guide 200 through its controller 203 and manipulator 202. In any case, disassociated devices are soft-locked in place by its respective controller.

The images captured by the camera instrument 211 are processed by an image processor 214 and displayed on a display screen 104 so as to provide a telepresence experience to the Surgeon, as described for example in U.S. Pat. No. 6,671,581 “Camera Referenced Control in a Minimally Invasive Surgical Apparatus,” which is incorporated herein by reference. Thus, a Surgeon using the medical robotic system 100 may perform a medical procedure on the Patient by manipulating input devices 108, 109 to cause corresponding movement of associated surgical tools 231, 241 while the Surgeon views images of the work site on the display screen 104.

Although described as a processor, it is to be appreciated that the processor 102 may be implemented in practice by any combination of hardware, software and firmware. Also, its functions as described herein may be performed by one unit or divided up among different components, each of which may be implemented in turn by any combination of hardware, software and firmware distributed throughout the system.

For additional details on the construction and operation of general aspects of a medical robotic system such as described herein, see, e.g., U.S. Pat. No. 6,493,608 “Aspects of a Control System of a Minimally Invasive Surgical Apparatus,” and U.S. Pat. Application Pub. No. U.S. 2008/007129 “Minimally Invasive Surgical System,” which are incorporated herein by reference.

FIGS. 3-4 respectively illustrate, as examples, top and right side views of a distal end of the entry guide 200 with the articulated camera instrument 211 and articulated surgical tool instruments 231, 241 extending outward. The articulated camera 211 extends through passage 321 and the articulated surgical tools 231, 241 respectively extend through passages 431, 441 of the entry guide 200. The camera 211 includes a tip 311, first, second, and third links 322, 324, 326, first and second joint assemblies (also referred to herein simply as “joints”) 323, 325, and a wrist assembly 327. The first joint assembly 323 couples the first and second links 322, 324 and the second joint assembly 325 couples the second and third links 324, 326 so that the second link 324 may pivot about the first joint assembly 323 in pitch and yaw while the first and third links 322, 326 remain parallel to each other.

The first and second joints 323, 325 are referred to as “joggle joints”, because they cooperatively operate together so that as the second link 324 pivots about the first joint 323 in pitch and/or yaw, the third link 326 pivots about the second joint 325 in a complementary fashion so that the first and third links 322, 326 always remain parallel to each other. The first link 322 may also rotate around its longitudinal axis in roll as well as move in and out (e.g., insertion towards the work site and retraction from the worksite) through the passage 321. The wrist assembly 327 also has pitch and yaw angular movement capability so that the camera's tip 311 may be oriented up or down and to the right or left, and combinations thereof.

The joints and links of the tools 231, 241 are similar in construction and operation to those of the camera 211. In particular, the tool 231 includes an end effector 331 (having jaws 338, 339), first, second, and third links 332, 334, 336, first and second joint assemblies 333, 335, and a wrist assembly 337 that are driven by actuators such as described in reference to FIG. 5 (plus an additional actuator for actuating the end effector 331). Likewise, the tool 241 includes an end effector 341 (having jaws 348, 349), first, second, and third links 342, 344, 346, first and second joint assemblies 343,345, and a wrist assembly 347 that are also driven by actuators such as described in reference to FIG. 5 (plus an additional actuator for actuating the end effector 341).

FIG. 5 illustrates, as an example, a diagram of interacting parts of an articulated instrument (such as the articulated camera 211 and the articulated surgical tools 231, 241) and its corresponding instrument manipulator (such as the camera manipulator 212 and the tool manipulators 232, 242). Each of the instruments includes a number of actuatable assemblies 521-523, 531-533, 570 for effectuating movement of the instrument (including its end effector), and its corresponding manipulator includes a number of actuators 501-503, 511-513, 560 for actuating the actuatable assemblies.

In addition, a number of interface mechanisms may also be provided. For example, pitch/yaw coupling mechanisms 540, 550 (respectively for the joggle joint pitch/yaw and the wrist pitch/yaw) and gear ratios 545, 555 (respectively for the instrument roll and the end effector actuation) are provided in a sterile manipulator/instrument interface to achieve the required range of motion of the instrument joints in instrument joint space while both satisfying compactness constraints in the manipulator actuator space and preserving accurate transmissions of motion across the interface. Although shown as a single block 540, the coupling between the joggle joint actuators 501, 502 (differentiated as #1 and #2) and joggle joint pitch/yaw assemblies 521, 522 may include a pair of coupling mechanisms—one on each side of the sterile interface (i.e., one on the manipulator side of the interface and one on the instrument side of the interface). Likewise, although shown as a single block 550, the coupling between the wrist actuators 512, 513 (differentiated as #1 and #2) and wrist pitch/yaw joint assemblies 532, 533 may also comprise a pair of coupling mechanisms—one on each side of the sterile interface.

Both the joggle joint pitch assembly 521 and the joggle joint yaw assembly 522 share the first, second and third links (e.g., links 322, 324, 326 of the articulated camera 211) and the first and second joints (e.g., joints 322, 325 of the articulated camera 211). In addition to these shared components, the joggle joint pitch and yaw assemblies 521, 522 also include mechanical couplings that couple the first and second joints (through joggle coupling 540) to the joggle joint pitch and yaw actuators 501, 502 so that the second link may controllably pivot about a line passing through the first joint and along an axis that is latitudinal to the longitudinal axis of the first link (e.g., link 322 of the articulated camera 211) and the second link may controllably pivot about a line passing through the first joint and along an axis that is orthogonal to both the latitudinal and longitudinal axes of the first link.

The in/out (I/O) assembly 523 includes the first link (e.g., link 322 of the articulated camera 211) and interfaces through a drive train coupling the in/out (I/O) actuator 503 to the first link so that the first link is controllably moved linearly along its longitudinal axis by actuation of the I/O actuator 503. The roll assembly 531 includes the first link and interfaces through one or more gears (i.e., having the gear ratio 545) that couple a rotating element of the roll actuator 511 (such as a rotor of a motor) to the first link so that the first link is controllably rotated about its longitudinal axis by actuation of the roll actuator 511.

The instrument manipulator (e.g., camera manipulator 212) includes wrist actuators 512, 513 that actuate through wrist coupling 550 pitch and yaw joints 532, 533 of the wrist assembly (e.g., wrist assembly 327 of the articulated camera 211) so as to cause the instrument tip (e.g., camera tip 311) to controllably pivot in an up-down (i.e., pitch) and side-to-side (i.e., yaw) directions relative to the wrist assembly. The grip assembly 570 includes the end effector (e.g., end effector 331 of the surgical tool 231) and interfaces through one or more gears (i.e., having the gear ratio 555) that couple the grip actuator 560 to the end effector so as to controllably actuate the end effector.

The group of instrument joints 500 is referred to as “translational joints” because by actuation of a combination of these joints, the instrument's wrist assembly may be positioned translationally within three-dimensional space using arc compensation as needed. The group of instrument joints 510 is referred to as “orientational joints” because by actuation of these joints, the instrument's tip may be oriented about the wrist assembly.

At various stages before, during, and after the performance of a medical procedure, there may be preferred poses for the articulated instruments 211, 231, 241 to best accomplish tasks performed at the time. For example, during normal operation, as shown in FIGS. 3 and 4, a preferred pose for each of the surgical tools 231, 241 may be an “elbow out, wrist in” pose to provide good range of motion while minimizing chances of inadvertent collisions with other instruments. Likewise, during normal operation, as shown in FIGS. 3 and 4, a preferred pose for the camera instrument 211 may be a “cobra” pose in which a good view of the end effectors 331, 341 of the surgical tool instruments 231, 241 is provided at the camera's image capturing end. As another example, when it is desired to retract an instrument back into the entry guide 200 to perform a tool exchange (i.e., exchange the instrument or its end effector for another instrument or end effector) or for reorienting the entry guide 200 by pivoting it about its remote center, a preferred pose for the instrument prior to its retraction into the entry guide 200 is a “straightened” pose wherein the links of the instrument are aligned in a straight line such as shown in FIG. 8.

FIG. 6 illustrates, as an example, a block diagram of the camera instrument controller (CTRLC) 213, which controls the posing (i.e., both translationally and orientationally) of the articulated camera instrument 211 as commanded by movement of the input device 108 by the Surgeon, when the input device 108 is selectively associated with the camera instrument 211 through the multiplexer 280 as previously described in reference to FIG. 1. The input device 108 includes a number of links connected by joints so as to facilitate multiple degrees-of-freedom movement. For example, as the Surgeon/operator moves the input device 108 from one position to another, sensors associated with the joints of the input device 108 sense such movement at sampling intervals (appropriate for the processing speed of the processor 102 and camera control purposes) and provide digital information 631 indicating such sampled movement in joint space to input processing block 610.

Input processing block 610 processes the information 631 received from the joint sensors of the input device 108 to transform the information into corresponding desired positions and velocities for the camera instrument 211 in its Cartesian space relative to a reference frame associated with the position of the Surgeon's eyes (the “eye reference frame”) by computing joint velocities from the joint position information and performing the transformation using a Jacobian matrix and eye related information using well-known transformation techniques.

Scale and offset processing block 601 receives the processed information 611 from the input processing block 610 and applies scale and offset adjustments to the information so that the resulting movement of the camera instrument 211 and consequently, the image being viewed on the display screen 104 appears natural and as expected by the operator of the input device 108. The scale adjustment is useful where small movements of the camera instrument 211 are desired relative to larger movements of the input device 108 in order to allow more precise movement of the camera instrument 211 as it views the work site. In addition, offset adjustments are applied for aligning the input device 108 with respect to the Surgeon's eyes as he or she manipulates the input device 108 to command movement of the camera instrument 211 and consequently, its captured image that is being displayed at the time on the display screen 104.

A simulated instrument block 604 transforms the commanded pose 621 of the camera instrument 211 from its Cartesian space to its joint space using inverse kinematics, limiting the commanded joint positions and velocities to avoid physical limitations or other constraints such as avoiding harmful contact with tissue or other parts of the Patient, and applying virtual constraints that may be defined to improve the performance of a medical procedure being performed at the time by the Surgeon using the medical robotic system 100. In particular, as illustrated in FIG. 9, the commanded pose 621 may be modified by virtual barrier logic 901 (described in more detail in reference to FIG. 15 below) which implements a virtual constraint on the commanded pose 621 to generate a modified commanded pose 623. Inverse kinematics and limiting block 902 then converts the modified commanded pose 623 from instrument Cartesian space to instrument joint space and limits the joint position and/or velocity to physical limitations or other constraints associated with or placed on the joints of the articulated camera instrument 211.

The output 622 of the simulated instrument block 604 (which includes a commanded value for each joint of the camera instrument 211) is provided to a joint control block 605 and a forward kinematics block 606. The joint controller block 605 includes a joint control system for each controlled joint (or operatively coupled joints such as “joggle joints”) of the camera instrument 211. For feedback control purposes, sensors associated with each of the controlled joints of the camera instrument 211 provide sensor data 632 back to the joint control block 605 indicating the current position and/or velocity of each joint of the camera instrument 211. The sensors may sense this joint information either directly (e.g., from the joint on the camera instrument 211) or indirectly (e.g., from the actuator in the camera manipulator 212 driving the joint). Each joint control system in the joint control block 605 then generates torque commands 633 for its respective actuator in the camera manipulator 212 so as to drive the difference between the commanded and sensed joint values to zero in a conventional feedback control system manner.

The forward kinematics block 606 transforms the output 622 of the simulated instrument block 604 from the camera instrument's joint space back to Cartesian space relative to the eye reference frame using forward kinematics of the camera instrument 211. The output 641 of the forward kinematics block 606 is provided to the scale and offset processing block 601 as well as back to the simulated instrument block 604 for its internal computational purposes.

The scale and offset processing block 601 performs inverse scale and offset functions on the output 641 of the forward kinematics block 606 before passing its output 612 to the input processing block 610 where an error value is calculated between its output 611 and input 612. If no limitation or other constraint had been imposed on the input 621 to the simulated instrument block 604, then the calculated error value would be zero. On the other hand, if a limitation or constraint had been imposed, then the error value is not zero and it is converted to a torque command 634 that drives actuators in the input device 108 to provide force feedback felt by the hands of the Surgeon. Thus, the Surgeon becomes aware that a limitation or constraint is being imposed by the force that he or she feels resisting his or her movement of the input device 108 in that direction.

A pose nudging block 625 is included in the controller 213 to generate a nudging force command 627 which is provided to the input processing block 610. The input processing block 610 then converts the nudging force command 627 into motor torques so that the commanded nudging force is felt by the Surgeon on the input device 108 in a manner that urges the Surgeon to command the pose of the camera instrument 211 to a preferred pose provided in pose data 626.

For the camera instrument 211, there may be at least two preferred poses. During normal mode operation, such as when the Surgeon is performing a medical procedure on a Patient, the preferred pose for the camera instrument 211 is the “cobra” pose shown in FIGS. 3 and 4. Looking downward at the “cobra” pose in FIG. 3, all links 322, 324, 326 of the camera instrument 211 are aligned with the longitudinal axis 401 of the first link 322 so that they have maximum available range of lateral motion and provide a reference for the main insertion direction of the camera instrument 211. Further, the joggle joints 323, 325 are “joggled up”, as shown in FIG. 4, so that the third link 326 is displaced a distance above the longitudinal axis 401 and the wrist assembly 327 is rotated at a negative pitch angle so that the camera tip 311 is oriented downwards at an angle so that the camera is preferably viewing the center of a workspace for the end effectors 331 and 341 of tool instruments 231 and 241, which are also extending out of the distal end of the entry guide 200 at the time. In this case, the Surgeon is preferably allowed to freely move the camera 211 forward and backward in the input/output (I/O) direction along the longitudinal axis 401 so that the camera 211 may better view the end effectors 331, 341 as they move away from and back towards the distal end of the entry guide 200 during their use.

During retraction mode, the preferred pose for the camera instrument 211 is the “straightened” pose. FIGS. 7 and 8 respectively illustrate simplified side views of the camera instrument 211 in the “cobra” and “straightened” poses. To go from the “cobra” pose to the “straightened” pose, the joggle joints 323, 325 rotate link 324 until it is aligned with the longitudinal axis 401 of the first link 322. Since the link 326 is always parallel to the first link 322 due to operation of the joggle joints 323, 325, when the link 324 is aligned with the longitudinal axis 401, the link 326 also is aligned with the longitudinal axis 401. Meanwhile, the wrist joint 327 also rotates the camera tip 311 until its central axis also aligns with the longitudinal axis 401.

FIG. 10 illustrates, as an example, a block diagram of the pose nudging block 625 and its coupling to the pose data block 626. In this example, the pose data block 626 comprises data stored in a non-volatile memory which is accessible to the processor 102. The stored data for the camera instrument 211 includes data for the “straightened” pose 1001 which is used for retraction of the camera instrument 211 and data for the “cobra” pose 1002 which is used during normal mode operation of the camera instrument 211.

The pose nudging block 625 comprises a retraction mode nudging block 1003, a normal mode nudging block 1004, and a summing node 1005. A key feature of the retraction and normal mode nudging blocks 1003 and 1004 is that nudging force commands from one is phased in while nudging force commands from the other is being phased out during a transition period. A more detailed description of the retraction mode nudging block 1003 is described in reference to FIG. 12 below and a more detailed description of the normal mode nudging block 1004 is described in reference to FIG. 13.

FIG. 12 illustrates, as an example, a block diagram of the retraction mode nudging block 1003 which continually processes incoming data. A summing node 1201 computes a difference (XERR, VERR) between the preferred “straightened” pose 1001 (i.e., the retraction configuration for the camera instrument 211) and the modified commanded pose (XSLV, VSLV) 623 which is generated by the virtual barrier logic 901 of the simulated instrument block 608 of the instrument controller 213. As used herein, the term “pose” means both position and orientation of the instrument as well as their positional and rotational velocities, so that the commanded pose may include both positional (XCMD) and velocity (VCMD) components, the modified commanded pose may include both positional (XSLV) and velocity (VSLV) components, the preferred pose may include both positional (XPP) and velocity (VPP) components, and the computed difference between the preferred pose and the modified commanded pose may include both positional (XERR) and velocity (VERR) components. In the computation performed in summing node 1201, however, the velocity (VPP) components of the preferred pose (VPP) are all presumed to be zero.

To explain how the modified commanded pose (XSLV, VSLV) is generated, an example of the virtual barrier logic 901 is described in reference to FIG. 15. In block 1501, the logic 901 receives the commanded pose (XCMD) 621 from the scale and offset block 621 and in block 1502, it determines the projection of the commanded pose 621 in a first direction, which in the present example is the instrument retraction direction along the longitudinal axis 401 of the first link 322 of the camera instrument 211. In block 1503, a determination is made whether the projection along the first direction would command the camera instrument 211 to move beyond a virtual barrier position. The virtual barrier position in this case is a position along the longitudinal axis 401 which is a threshold distance or safety margin from the distal end of the entry guide 200. As described in US 2011/0040305 A1, the purpose of the safety margin is to prevent damage from occurring to either or both the entry guide 200 and the articulated instrument 211 when attempting to force the articulated instrument 211 back into the entry guide 200 while it is in a configuration in which it physically will not fit at the time. If the determination in block 1503 is NO, then the virtual barrier logic 901 jumps back to block 1501 to process data for a next process cycle. On the other hand, if the determination in block 1503 is YES, then in block 1504, the current pose of the camera instrument 211 is determined sensing its joint positions and applying forward kinematics to determine their corresponding Cartesian pose. In block 1505, a determination is then made whether the current pose of the camera instrument 211 is the preferred pose (i.e., “straightened” pose in this case). If the determination in block 1505 is YES, then the virtual barrier logic 901 doesn't modify the commanded pose (XCMD) and jumps back to block 1501 to process data for a next process cycle. On the other hand, if the determination n block 1505 is NO, then commanded pose (XCMD) is modified by applying the virtual barrier as constraint so that the camera instrument 211 is prevented from moving further in the first direction. The method then loops back to block 1501 to process data for the next process cycle. Thus, the camera instrument 211 is prevented in this way from moving beyond the virtual barrier position until the current pose is the preferred retraction pose of the camera instrument 211.

Referring back to FIG. 12, in block 1202, non-nudging components of the calculated difference (XERR, VERR) are removed. In particular, translational components along the first direction and the roll rotational component about the tip 310 are removed since neither of these components affects the preferred pose (i.e., regardless of their values, the camera instrument may be placed in a “straightened” pose as shown in FIG. 8). In block 1203, the modified difference (XERR′, VERR′) generated in block 1202 is converted to generate a force command that would result in one or more forces being applied to the input device 108 so that the Surgeon is urged to command the camera instrument 211 to the preferred pose. Preferably such force command is a visco-elastic six degree-of-freedom force that would be applied to corresponding degrees-of-freedom of the input device 108.

An example of the force converter block 1203 is illustrated in FIG. 14 by a block diagram of a Proportional-Derivative (PD) open loop system. In this PD system, the modified position difference (XERR′) is multiplied by a position gain (KP) 1401 and limited by limiter 1402 to a first saturation value (SATP) to generate a first force command contribution. At the same time, the modified velocity difference (VERR′) is multiplied by a derivative gain (KD) 1403 to generate a second force command contribution. A summing node 1404 calculates a difference between second and first force command contributions and a limiter 1405 limits to the difference to a second saturation value (SATF). The thus limited difference between the second and first force command contributions results in a visco-elastic six degree-of-freedom Cartesian force for nudging the Surgeon to move the input device 108 so as to command the preferred pose. Values for the first and second saturation values are selected so as to ensure that commanded motor torques on the motors of the input device 108 do not exceed their rated maximum values.

Referring back to FIG. 12, modulator 1207 amplitude modulates the visco-elastic six degree-of-freedom Cartesian force generated by the force converter block 1203 with a retraction activation signal which resembles curve 1101 in FIG. 11. To generate the retraction activation signal, a summing node 1204 calculates a difference between the commanded pose (XCMD) and the modified commanded pose (XSLV), ignoring velocity contributions, modulation coefficients generator 1205 generates a stream of modulation coefficients using the calculated difference, and a low-pass filter 1206 filters the stream of modulation coefficients.

An example of the generation of the retraction mode activation signal is provided in a flow diagram illustrated in FIG. 16. Blocks 1601 and 1602 describe actions taken by the summing node 1204. In particular, in block 1601, the commanded pose (XCMD) and modified commanded pose (XSLV) are received, and in block 1602, a difference between the commanded pose (XCMD) and the modified commanded pose (XSLV) is calculated. Blocks 1603 to 1607 next describe actions taken by the modulation coefficients generator 1205. In block 1603, a projection of the calculated difference in a first direction (i.e., the retraction direction along the longitudinal axis 401) is determined and in block 1604, a determination is made whether the projection exceeds a threshold value. The threshold value in this case should be large enough to ensure that the Surgeon really intends to retract the camera instrument 211 and that it is not an inadvertent action such as may result from hand tremor. If the determination in block 1604 is YES, then in block 1605, the current modulation coefficient is set to an integer value “1”. On the other hand, if the determination in block 1604 is NO, then in block 1606, the current modulation coefficient is set to an integer value of “0”. In block 1607, the current modulation coefficient is then appended to a stream of modulation coefficients generated in prior process periods. Block 1608 describes action taken by the low-pass filter 1206. In particular, in block 1608, the retraction activation signal is generated by passing the stream of modulation coefficients through the low-pass filter 1206 and the process then jumps back to block 1601 to process data for the next process cycle.

FIG. 13 illustrates, as an example, a block diagram of the normal mode nudging block 1004 which also continually processes incoming data. A summing node 1301 computes a difference (XERR, VERR) between the preferred “cobra” pose 1002 (i.e., the normal mode configuration for the camera instrument 211) and the modified commanded pose (XSLV, VSLV) 623 which is generated by the virtual barrier logic 901 of the simulated instrument block 608 of the instrument controller 213.

In block 1302, non-nudging components of the calculated difference (XERR, VERR) are removed. In particular, translational components along the first direction and the roll rotational component about the tip 311 are removed since neither of these components affects the preferred pose (i.e., regardless of their values, the camera instrument may be placed in a “cobra” pose as shown in FIG. 7). In block 1303, the modified difference (XERR′, VERR′) generated in block 1302 is converted to generate a force command that would result in one or more forces being applied to the input device 108 so that the Surgeon is urged to command the camera instrument 211 to the preferred pose. Preferably such force command is a visco-elastic six degree-of-freedom force that would be applied to corresponding degrees-of-freedom of the input device 108, whose generation is similar to that previously described in reference to FIG. 14.

Modulator 1307 then amplitude modulates the visco-elastic six degree-of-freedom Cartesian force generated by the force converter block 1303 with a normal mode deactivation signal which resembles curve 1102 in FIG. 11. To generate the normal mode deactivation signal, a summing node 1304 calculates a difference between the commanded pose (XCMD) and the modified commanded pose (XSLV), ignoring velocity contributions, modulation coefficients generator 1305 generates a stream of modulation coefficients using the calculated difference, and a low-pass filter 1306 filters the stream of modulation coefficients.

An example of the generation of the normal mode deactivation signal is provided in a flow diagram illustrated in FIG. 17. Blocks 1701 and 1702 describe actions taken by the summing node 1304. In particular, in block 1701, the commanded pose (XCMD) and modified commanded pose (XSLV) are received, and in block 1702, a difference between the commanded pose (XCMD) and the modified commanded pose (XSLV) is calculated. Blocks 1703 to 1707 next describe actions taken by the modulation coefficients generator 1305. In block 1703, a projection of the calculated difference in a first direction (i.e., the retraction direction along the longitudinal axis 401) is determined and in block 1704, a determination is made whether the projection exceeds a threshold value. The threshold value in this case should be large enough to ensure that the Surgeon really intends to retract the camera instrument 211 and that it is not inadvertent action such as may result from hand tremor. If the determination in block 1704 is YES, then in block 1705, the current modulation coefficient is set to an integer value “0”. On the other hand, if the determination in block 1704 is NO, then in block 1706, the current modulation coefficient is set to an integer value of “1”. Note that the modulation coefficient value assignments are opposite to those used in the generation of the retraction activation signal, which results in one of the retraction and normal mode activation signals phasing in while the other is phasing out. In block 1707, the current modulation coefficient is then appended to a stream of modulation coefficients generated in prior process periods. Block 1708 finally describes action taken by the low-pass filter 1306. In particular, in block 1708, the normal mode deactivation signal is generated by passing stream of modulation coefficients through the low-pass filter 1306. The process then jumps back to block 1701 to process data for the next process cycle.

The time constants for the low-pass filter 1206 in the retraction mode nudging block 1003 and the low-pass filter 1306 in the normal mode nudging block 1004 are preferably the same so that the phasing in and phasing out match during the transition period such as shown in FIG. 11, where time “t(k)” represents the time that the threshold value determinations in blocks 1804 and 1704 first result in a YES determination, time “t(k-m)” represents a time prior to “t(k)” when the threshold value determinations in blocks 1804 and 1704 resulted in a NO determination, and time “t(k+m)” represents a time after “t(k)” when the threshold value determinations in blocks 1804 and 1704 still result in a YES determination.

FIG. 18 illustrates a flow diagram summarizing the first embodiment of the invention as described in detail above. In block 1801, a commanded pose (XCMD) is received from an input device associated at the time with the articulated instrument whose pose is being commanded. In block 1802, the commanded pose is modified using virtual constraints (such as described in reference to FIG. 15). In blocks 1803-1807, a first force command is generated which is to be phased in to nudge the operator of the input device to command a first (new) preferred pose (such as described in reference to FIG. 12) while concurrently in blocks 1808-1812, a second force command is generated which is to be phased out to nudge the operator of the input device to command a second (incumbent) preferred pose (such as described in reference to FIG. 13). In block 1813, the first and second force commands are applied to the input device so that initially the operator of the input device is urged to command the second preferred pose then subsequently after a phasing in and phasing out transition period the operator is urged to command the first preferred pose.

FIGS. 19-21 illustrate additional embodiments of the invention which include various combinations of some, but not all of the blocks described in reference to FIG. 18. In particular, FIG. 19 illustrates a second embodiment that is a modification to the first embodiment, wherein the commanded pose is not modified using virtual constraints by deleting block 1802, but performing all other blocks of the first embodiment. FIG. 20 illustrates a third embodiment that is a modification to the first embodiment, wherein a second (incumbent) preferred pose is not active by deleting blocks 808-812, but performing all other blocks of the first embodiment with block 813 modified since there is no second force command to be phased out. FIG. 21 illustrates a fourth embodiment that is a modification to the third embodiment, wherein the commanded pose is not modified using virtual constraints by deleting block 1802, but performing all other blocks of the third embodiment.

FIGS. 22-24 illustrate still other embodiments of the invention which expand upon some of the previously disclosed embodiments. In particular, whereas prior embodiments disclose a single preferred pose being active at a time (outside a transition period), the embodiments shown in FIGS. 22-24 contemplate the possibility of multiple preferred poses being active at a time with the active preferred poses being weighted so that one or some may be more dominant than others. Further, the weightings provide an additional mechanism through which preferred poses may be transitioned in and out by making their respective weightings dynamically alterable (e.g., progressively changing from a weighting of “0” to a weighting of “1” to phase the corresponding preferred pose in and conversely, progressively changing from a weighting of “1” to a weighting of “0” to phase the corresponding preferred pose out). Also, whereas prior embodiments disclose fixed preferred poses for different operating modes, the embodiments shown in FIGS. 22-24 contemplate the possibility of dynamically changing preferred poses based upon system data such as the current or commanded poses of other articulated instruments. For example, the preferred pose for the camera instrument 211 may dynamically change as the poses of the end effectors 331, 341 of the tool instruments 231, 241 change so that the end effectors 331, 341 remain well positioned in a field of view of the camera instrument 211. As another example, the preferred poses of each of the articulated instruments 211, 231, 241 may dynamically change to avoid collisions with others of the articulated instruments 211, 231, 241 during the performance of a medical procedure using the articulated instruments 211, 231, 241.

FIG. 22 illustrates, for example, a block diagram of an alternative instrument controller for operator commanded movement of an articulated instrument. Although the example is for the camera controller 213, it is to be appreciated that the same general structure may be used for other device controllers 203, 233, 243 in the medical robotic system 100. The functions of blocks 610, 601, 605, 606 are the same as previously described in reference to FIG. 6. The function of the simulated instrument block 2204 is generally the same as block 604 of FIG. 6 with regards to inverse kinematics and limiting, but may differ in regards to virtual constraints imposed on the commanded pose 621 to generate a modified commanded pose 2205, because of different operating modes and/or preferred poses. Likewise, the function of pose nudging block 2201 is generally the same as block 625 with regards to summing together two pose nudging contributions wherein a first (new) preferred pose is to be phased in while a second (incumbent) preferred pose is to be phased out according to respective activation signals.

A pose generator block 2202 is included in the controller 213 to dynamically generate one or more preferred poses that are provided to the pose nudging block 2201, as well as pass through static preferred poses when appropriate. In particular, although a static preferred pose provided by the pose data block 626 may be normally passed through, the preferred pose for the articulated camera instrument 211 may dynamically be changed from the static preferred pose as conditions, such as the poses of other tool instruments 231, 241 around it, change. As one example, the preferred pose for the camera instrument 211 may dynamically change during normal operating mode to avoid collisions with the tool instruments 231, 241, which are being used and therefore, moving at the time to perform a medical procedure on a patient anatomy. To dynamically generate one or more preferred poses to be phased in (such as preferred poses 2301, 2303, 2305 of FIG. 23) and one or more preferred poses to be phased out (such as preferred poses 2401, 2403, 2405), the pose generator block 2202 may use a different function of one or more states of the system for each of the preferred poses to be dynamically changed. The system state information in this case is provided by system data 2203. As one example, the system data 2203 may comprise the commanded poses of other instruments 231, 241 in the system 100. As another example, the system data 2203 may comprise the actual poses of the other instruments 231, 241 as determined by applying forward kinematics to their sensed joint positions.

The pose nudging block 2201 includes “phase-in” and “phase-out” nudging blocks which respectively generate nudging forces that are to be phased-in and phased-out on the input device 108 in a similar manner as previously described with respect to the retraction mode and normal mode nudging blocks, 1003 and 1004, of FIG. 10.

FIG. 23 illustrates, as an example, a block diagram of the “phase-in” nudging block. A preferred pose 2320 is generated by a weighted average of a plurality of preferred poses (e.g., preferred poses 2301, 2303, 2305) so that each of the preferred poses is multiplied by a corresponding weight (e.g., weights 2302, 2304, 2306) with the sum of the weights equal to “1”. The weights may be fixed values or preferably dynamic values so one or more of the preferred poses may be dominant at different times, in different operating modes or under different system conditions. A difference between the preferred pose 2320 and the modified commanded pose 2205 is computed by summing node 2314. Non-nudging components of the difference are removed in block 2315 and the result provided to force converter block 2316 which generates a force command such as described in reference to block 1203 of FIG. 12. A phase-in activation signal is generated by phase-in signal generator block 2317 so as to resemble the retraction mode activation signal 1101 in FIG. 1I. An amplitude modulated force command, which is to be phased-in on the input device 108, is then generated by amplitude modulator 2318 by amplitude modulating the force command generated by the force converter block 2316 with the phase-in activation signal.

Using a similar construction, FIG. 24 illustrates, as an example, a block diagram of the “phase-out” nudging block. A preferred pose 2420 in this case is generated by a weighted average of a plurality of preferred poses (e.g., preferred poses 2401, 2403, 2405) so that each of the preferred poses is multiplied by a corresponding weight (e.g., weights 2402, 2404, 2406) with the sum of the weights equal to “1”. The weights may be fixed values or preferably dynamic values so one or more of the preferred poses may be dominant at different times, in different operating modes or under different system conditions. A difference between the preferred pose 2420 and the modified commanded pose 2205 is computed by summing node 2414. Non-nudging components of the difference are removed in block 2415 and the result provided to force converter block 2416 which generates a force command such as described in reference to block 1203 of FIG. 12. A phase-out activation signal is generated by phase-out signal generator block 2417 so as to resemble the normal mode activation signal 1102 in FIG. 11. An amplitude modulated force command, which is provided to and is to be phased-out on the input device 108, is then generated by amplitude modulator 2418 by amplitude modulating the force command generated by the force converter block 2416 with the phase-out activation signal.

In addition to the embodiments described herein, it is to be appreciated that other embodiments may be constructed, and are fully contemplated to be within the scope of the present invention, through different combinations of their various teachings. In particular, although the various aspects of the present invention have been described with respect to preferred and alternative embodiments, it will be understood that the invention is entitled to full protection within the full scope of the appended claims. 

What is claimed is:
 1. A method for urging operator manipulation of an input device to command an articulated instrument to a preferred pose, the method comprising: generating a commanded pose of the articulated instrument in response to operator manipulation of the input device; modifying the commanded pose by applying a virtual barrier as a constraint to prevent the articulated instrument from being commanded to move beyond the virtual barrier until at least a portion of the articulated instrument which is closest to, but has not yet encountered the virtual barrier conforms with a first preferred pose; generating a stream of modulation coefficients indicative of a difference between the commanded pose and the modified commanded pose; generating a first activation signal by processing the stream of modulation coefficients; generating first force commands for a first plurality of degrees of freedom of the input device so as to be indicative of a difference between the first preferred pose and the commanded pose; and applying the first force commands to the first plurality of degrees of freedom of the input device by phasing in their application according to the first activation signal.
 2. The method of claim 1, wherein generating the first activation signal comprises filtering the stream of modulation coefficients by using a low pass filter.
 3. The method of claim 1, wherein the constraint prevents the articulated instrument from being commanded to move beyond the virtual barrier in a first direction, and wherein generating the stream of modulation coefficients comprises: determining a difference between the commanded pose and the modified commanded pose, projecting the difference along the first direction, and binary coding the projected difference by setting a current modulation coefficient to a first value when the projected difference is greater than a threshold value and setting the current modulation coefficient to a second value when the projected difference is less than or equal to the threshold value.
 4. The method of claim 1, wherein the constraint prevents the articulated instrument from being commanded to move beyond the virtual barrier in a first direction, and wherein generating the first force commands comprises: comparing the first preferred pose to the modified commanded pose to generate Cartesian position and velocity errors; modifying the Cartesian position and velocity errors by removing components along the first direction and about an axis of a pivotable tip of the articulated instrument; and generating a visco-elastic six degree-of-freedom force command using the modified Cartesian position and velocity errors.
 5. The method of claim 4, wherein generating of the visco-elastic six degree-of-freedom force command comprises: amplifying the modified Cartesian position error by a position gain to generate a first result and limiting the first result to a position saturation limit to generate a second result; amplifying the modified Cartesian velocity error by a velocity gain to generate a third result; generating an interim visco-elastic six-degree-of-freedom force command by subtracting the third result from the second result; and generating the visco-elastic six degree-of-freedom force command by limiting the interim visco-elastic six-degree-of-freedom force command to a force saturation limit.
 6. The method of claim 4, wherein applying the first force commands to the first plurality of degrees of freedom of the input device by phasing in their application according to the first activation signal comprises: amplitude modulating the visco-elastic six degree-of-freedom force command with the first activation signal.
 7. The method of claim 1, further comprising: generating second force commands for a second plurality of degrees of freedom of the input device so as to be indicative of a difference between a second preferred pose and the commanded pose; applying the second force commands to the second plurality of degrees of freedom of the input device prior to phasing in the application of the first force commands according to the first activation signal; and phasing out application of the second force commands according to a second activation signal.
 8. The method of claim 7, wherein the constraint prevents the articulated instrument from being commanded to move beyond the virtual barrier in a first direction, the method further comprising: generating a second stream of modulation coefficients by determining a difference between the commanded pose and modified commanded pose, projecting the difference along the first direction, and binary coding the projected difference by setting a current modulation coefficient to a second value when the projected difference is greater than a threshold value and setting the current modulation coefficient to a first value when the projected difference is less than or equal to the threshold value; and generating the second activation signal by filtering the second stream of modulation coefficients.
 9. The method of claim 7, wherein the first and second activation signals are complementary signals so that the first activation signal is phased in as the second activation signal is phased out.
 10. A robotic system comprising: an input device; an articulated instrument; and a processor programmed to: generate a commanded pose of the articulated instrument in response to operator manipulation of the input device, modify the commanded pose by applying a virtual barrier as a constraint to prevent the articulated instrument from being commanded to move beyond the virtual barrier until at least a portion of the articulated instrument which is closest to, but has not yet encountered the virtual barrier conforms with a first preferred pose, generate a stream of modulation coefficients indicative of a difference between the commanded pose and the modified commanded pose, generate a first activation signal by processing the stream of modulation coefficients, generate first force commands for a plurality of degrees of freedom of the input device so as to be indicative of a difference between the first preferred pose and the commanded pose, and command application of the first force commands on the plurality of degrees of freedom of the input device so as to phase in their application according to the first activation signal.
 11. The system of claim 10, wherein the processor is programmed to generate the first activation signal by filtering the stream of modulation coefficients by using a low pass filter.
 12. The system of claim 10, wherein the constraint prevents the articulated instrument from being commanded to move beyond the virtual barrier in a first direction, and wherein the processor is programmed to generate the stream of modulation coefficients by: determining a difference between the commanded pose and the modified commanded pose, projecting the difference along the first direction, and binary coding the projected difference by setting a current modulation coefficient to a first value when the projected difference is greater than a threshold value and setting the current modulation coefficient to a second value when the projected difference is less than or equal to the threshold value.
 13. The system of claim 10, wherein the constraint prevents the articulated instrument from being commanded to move beyond the virtual barrier in a first direction, and wherein the processor is programmed to generate the first force commands by: comparing the first preferred pose to the modified commanded pose to generate Cartesian position and velocity errors, modifying the Cartesian position and velocity errors by removing components along the first direction and about an axis of a pivotable tip of the articulated instrument, and generating a visco-elastic six degree-of-freedom force command using the modified Cartesian position and velocity errors.
 14. The system of claim 13, wherein the processor is programmed to generate the visco-elastic six degree-of-freedom force command by: amplifying the modified Cartesian position error by a position gain to generate a first result and limiting the first result to a position saturation limit to generate a second result, amplifying the modified Cartesian velocity error by a velocity gain to generate a third result, generating an interim visco-elastic six-degree-of-freedom force command by subtracting the third result from the second result, and generating the visco-elastic six degree-of-freedom force command by limiting the interim visco-elastic six-degree-of-freedom force command to a force saturation limit.
 15. The system of claim 13, wherein the processor is programmed to command application of the first force commands on the plurality of degrees of freedom of the input device so as to phase in their application according to the first activation signal by generating an amplitude modulated force by amplitude modulating the visco-elastic six degree of freedom force with the first activation signal and commanding application of the amplitude modulated force on input device.
 16. The system of claim 10, wherein the processor is programmed to generate second force commands for a plurality of degrees of freedom of the input device so as to be indicative of a difference between a second preferred pose and the commanded pose; apply the second force commands to the plurality of degrees of freedom of the input device prior to phasing in the application of the first force commands according to the first activation signal; and phase out application of the second force commands according to a second activation signal.
 17. The system of claim 16, wherein the constraint prevents the articulated instrument from being commanded to move beyond the virtual barrier in a first direction, wherein the processor is programmed to generate a second stream of modulation coefficients by determining a difference between the commanded pose and the modified commanded pose, projecting the difference along the first direction, and binary coding the projected difference by setting a current modulation coefficient to a second value when the projected difference is greater than a threshold value and setting the current modulation coefficient to a first value when the projected difference is less than or equal to the threshold value, and wherein the processor is programmed to generate the second activation signal by filtering the second stream of modulation coefficients.
 18. The system of claim 17, wherein the first and second activation signals are complementary signals so that the first activation is phased in as the second activation signal is phased out.
 19. The system of claim 10, wherein the processor is programmed to generate the first preferred pose by using a weighted average of a first plurality of preferred poses, and wherein at least one of the first plurality of preferred poses is a function of at least one state of the system.
 20. A non-transient computer readable medium containing program instructions for causing a computer to perform the method of: generating a commanded pose of an articulated instrument in response to operator manipulation of an input device; modifying the commanded pose by applying a virtual barrier as a constraint to prevent the articulated instrument from being commanded to move beyond the virtual barrier until at least a portion of the articulated instrument which is closest to, but has not yet encountered the virtual barrier conforms with a first preferred pose; generating a stream of modulation coefficients indicative of a difference between the commanded pose and the modified commanded pose; generating a first activation signal by processing the stream of modulation coefficients; generating first force commands so as to be indicative of a difference between the first preferred pose and the commanded pose; and applying the first force commands to the input device by phasing in their application according to the first activation signal. 